Allow parallel irrigation (Sprinkler integration)

**Describe the problem you have/What new integration you would like**
I'd like to be able to start zones in parallel with auto-advance.
Note: This is not the same as #1982, as I'd like to have different durations for the zones, so I can't make it a group as suggested there.

**Please describe your use case for this integration and alternatives you've tried:**
- I have a drip line, which has very low flow but needs to stay on for quite some time. I'd like to activate that while the different lawn irrigation zones are active (with auto-advance) in order to minimize pump run time, saving on energy cost.
- I have two zones with lower flow requirements. Want to run them in parallel to save irrigation time and again energy cost of pump runtime.

**Additional context**
A possible way of implementation (inspired by MS Powerpoint's "start with previous" setting in animation timing editor):
Add boolean parameter "is_parallel" to a valve configuration. If set to true, the auto-advance feature will activate the next valve in sequence immediately when the current one becomes active.

In other words, "is_parallel" determines, whether auto-advance should proceed in the sequence when then irrigation of the given zone _ends_ (is_parallel = false, default) or _start_ (is_parallel = true).

In my use case I'd then be able to configure the drip line as follows:
```
sprinkler:
...
valves:
- valve_switch: "Drip line"
is_parallel: true
- valve_switch: "Lawn 1"
- valve_switch: "Lawn 2"
- valve_switch: "Lawn 3"
```

"Drip line" is activated first in sequence, as usual. With auto-advance on and "is_parallel" is set, "Lawn 1" shall be activated immediately as well. When "Lawn 1" is done, auto-advance will activate "Lawn 2", and so on. Drip line has a much longer duration an will keep running along with Lawn 1, 2 and 3. When "Drip line" is done, nothing happens.